2,3-DCP is used in quantities as an intermediate for synthesizing epichlorohydrin useful as a solvent, a starting material for epoxy resins, a starting material for synthetic rubber, a stabilizer for chlorinated rubber, etc.
Conventional production and purification of 2,3-DCP is illustrated in the system diagram of FIG. 5. In FIG. 5, a hydrochloric acid aqueous solution (HClaq) and allyl alcohol (AAL) are charged in reactor 1 equipped with stirrer 1a, and chlorine gas is blown through the AAL solution in the HClaq while cooling the solution at a constant temperature to produce 2,3-DCP. The reaction mixture is forwarded to degassing tower 2, where hydrogen chloride is evolved and returned to reactor 1. The degassed mixture is then delivered to first decanter 3, where it is separated into aqueous layer 3a and oily layer 3b by cooling to 40.degree. C. or lower. Aqueous layer 3a is recycled to reactor 1, while oily layer 3b is recovered for direct use as a raw material for other compounds or purified to recover 2,3-DCP therefrom. For the conventional production of 2,3-DCP, reference can be made to U.S. Pat. No. 4,634,784.
Oily layer 3b comprises 72 to 75% by weight of 2,3-DCP, 3 to 6% by weight of by-products, e.g., glycerin monochlorohydrin and oligomers, and about 20% by weight of HClaq as an azeotropic component (20%).
For the production of epichlorohydrin, 2,3-DCP is once recovered from oily layer 3b and saponified by reaction with a calcium hydroxide aqueous solution, or oily layer 3b as separated in decanter 3 is directly subjected to saponification.
The former process in which the oily layer is purified involves an extra cost for separation into components and treatment of unnecessary and harmful components.
The latter process in which the oily layer is saponified as such is economically disadvantageous in that useful by-products such as glycerin monochlorohydrin cannot be recovered because they are incorporated into the waste liquor of the saponification mixture. Further, the hydrochloric acid contained in the oily layer is concurrently neutralized with calcium hydroxide, leading to not only wasteful consumption of calcium hydroxide but also necessity of making up for the loss of hydrochloric acid which is withdrawn from the chlorination system and is never recovered.